1. Field of the Invention
The present invention relates to a method of allocating bandwidth using a Resilient Packet Ring (RPR) fairness mechanism and to a program storage device, readable by a machine, tangibly embodying a program of instructions executable by the machine to perform a method of allocating bandwidth using a Resilient Packet Ring (RPR) fairness mechanism.
2. Description of the Related Art
The current Internet can be classified into three parts, namely, a subscriber network, a metro network and a backbone network. Although the subscriber and backbone networks have been developed to accommodate Internet traffic which has abruptly increased recently, the metro network connecting two networks to each other is constructed as a ring network of a SONET/SDH (Synchronous Optical Network/Synchronous Digital Hierarchy) scheme which is an existing circuit switching scheme. Accordingly, bandwidth is not being used efficiently.
Therefore, a bottleneck occurs in the current metro network and an imbalance of speed occurs in an entire network structure. A metro Ethernet of a packet switching scheme has been suggested as technology to make up for the disadvantages of the SONET/SDH net.
However, although the metro Ethernet has a great merit in that traffic of the current Internet is in packets, it has disadvantages in that a high-speed protection mechanism provided in a point-to-point ring network or mesh topology SONET network cannot be provided since most current metro networks have a ring topology configuration.
Furthermore, the Ethernet also has disadvantages in that it is difficult to embody a mechanism for entire fairness in sharing the bandwidth of the ring. An IEEE 802.17 Resilient Packet Ring (RPR) of a protocol in layer 2 has been suggested as a technology for transmitting the traffic with more efficiency in the metro network by making up for the disadvantages of the existed metro network.
An RPR fairness mechanism is defined in the RPR scheme so that all of the nodes of the ring can fairly use the bandwidth of the ring.
All nodes of the RPR are connected to a dual ring and Media Access Control (MAC) protocols are independently operated for the two rings. The RPR MAC provides Class-A (High Priority), Class-B (Medium Priority) and Class-C (Low Priority) services in accordance with the priority of the traffic. Also, the Class-B service is divided into traffic which observes a predefined Committed Information Rate (CIR) and traffic which does not observe the predefined CIR. The CIR observing traffic is processed in the same manner as the Class-A traffic, and the CIR violating traffic is called an Excess Medium Priority (eMP) traffic and is processed in the same manner as the Class-C traffic.
Only the eMP and Class-C traffic described above are applied to the RPR fairness mechanism. The RPR MAC has addA, addB and addC transmission buffers.
Also, all kinds of control traffic are transmitted to the ring through the addMac transmission buffer in order to control the ring. The nodes in the RPR have ring configurations so that each of the nodes has to perform a role of a transit node which transmits the traffic transmitted by a source node to a destination node.
Accordingly, there are two transit buffers, namely, a Primary Transit Queue (PTQ) and a Secondary Transit Queue (STQ) in the RPR MAC in order to perform the role of a transit node. Also, the STQ transit buffer has two threshold values, a high_threshold and a low_threshold, to find and control congestion. The Class-A traffic from an upstream node is transmitted to a downstream node through the PTQ transit buffer and the Class-B and Class-C traffic from the upstream node are transmitted to the downstream node through the STQ transit buffer.
The RPR fairness mechanism is driven by monitoring an amount of traffic transmitted by an MAC client of the node and an amount of the Class-C and eMP traffic transmitted from the upstream node, and has following parameters in order to control amounts of such traffic.
addRate: measuring the amount of the Class-C and eMP traffic transmitted from its client to a ring.
addRateCongested: measuring the amount of the addRate traffic transmitted from its client to the ring and transmitted to a downstream node after a node in which congestion has occurred.
fwRate: measuring the amount of the Class-C and eMP traffic transmitted to the ring through its STQ transit buffer.
fwRateCongested: measuring the amount of fwRate traffic transmitted to the ring through its STQ transit buffer and transferred to a downstream node after a node in which congestion has occurred.
allowedRateCongested: measuring the amount of the maximum addRate traffic transmitted to the downstream node after a node in which the congestion has occurred. When congestion does not occur in the downstream node, that is, when a fairness transmission rate of a FULL value is received from the downstream node, this value is increased at intervals.
Each of the nodes checks its STQ buffer every aging interval. When the amount of the traffic exceeds the low_threshold, congestion has occurred in the node, and a fair rate and its MAC address are carried on the fairness message and transmitted to an upstream node when a current advertisement interval is completed.
The upstream node which received the fairness message reestablishes its allowedRateCongested value as a fairness transmission rate of the received fairness message. That is, the node which received the fairness message transmits the amount of traffic (Class-C+eMP) transmitted by the node during the next aging interval so as not to exceed the received fairness transmission rate so that the congestion does not occur.
That is, when the amount of addRate (Class-C+eMP) transmitted by a node due to the traffic transmitted from the upstream node is reduced, that node advertises the reduced addRate to the upstream nodes using the fairness message. The upstream nodes which have received this fairness message control their transmission rates so as not to exceed the received fairness transmission rate, and are arranged so that when the traffic inputted from the upstream node is reduced, the addRate of the node in which the congestion has occurred is increased again so that the congestion is resolved.
All nodes of the RPR network transmit the fairness message whenever an advertised interval is completed, and the fairness message includes a fairness transmission rate of a node in which congestion occurs most severely and an MAC address of its node, and the fairness message is transmitted to the upstream nodes in a hop-by-hop scheme. The transmitted fairness transmission rate is the amount of the addRate (Class-C+eMP) which the node in which the congestion currently occurs most severely has transmitted during the previous aging interval.
As described above, the RPR fairness mechanism discussed above has problems in that congestion occurs and the bandwidth which is not used but available is not efficiently used after the congestion has been solved so that the bandwidth usage ratio is low.
The following patents each discloses features in common with the present invention but do not teach or suggest the inventive features specifically recited in the present application: U.S. Patent Application No. 2003/0163593 to Knightly, entitled METHOD AND SYSTEM FOR IMPLEMENTING A FAIR, HIGH-PERFORMANCE PROTOCOL, FOR RESILIENT PACKET RING NETWORKS, published on Aug. 28, 2003; U.S. Patent Application No. 2003/0035371 to Reed et al., entitled MEANS AND APPARATUS FOR A SCALEABLE CONGESTION FREE SWITCHING SYSTEM WITH INTELLIGENT CONTROL, published on 20 Feb. 2003; U.S. Patent Application No. 2004/0100984 to Nam et al., entitled RESOURCE ALLOCATION METHOD FOR PROVIDING LOAD BALANCING AND FAIRNESS FOR DUAL RING, published on May 27, 2004; U.S. Patent Application No. 2004/0032826 to Sridhar, entitled SYSTEM AND METHOD FOR INCREASING FAIRNESS IN PACKET RING NETWORKS published on Feb. 19, 2004; and U.S. Patent Application No. 2004/0103179 to Damm et al., entitled TOPOLOGY MANAGEMENT OF DUAL RING NETWORK, published on May 27, 2004.